OVEREXPRESSION OF HOX11 LEADS TO THE IMMORTALIZATION OF EMBRYONIC PRECURSORS WITH BOTH PRIMITIVE AND DEFINITIVE HEMATOPOIETIC POTENTIAL

Primitive and definitive erythropoiesis represent distinct hematopoiet ic programs that differ with respect to stage of development, transcri ptional control, and growth regulation. Although these differences hav e been recognized for some time, the relationship of the two erythroid lineages to each other is not well established. We have used a model system based on the hematopoietic development of embryonic stem (ES) c ells in culture to investigate the origins of the earliest hematopoiet ic populations. Using ES cells transduced with a retrovirus that overe xpresses the HOX11 gene, we have established factor-dependent hematopo ietic cell lines that represent novel stages of embryonic hematopoiesi s, Analysis of three of these cell lines indicates that they differ wi th respect to cytokine responsiveness, cell surface markers, and devel opmental potential. Two of the cell lines, EBHX1 and EBHX11, display t he unique capacity to generate both primitive and definitive erythroid progeny as defined by morphology and expression of beta H1 and beta m ajor globin, The third line, EBHX14, has definitive erythroid and myel oid potential, I,ut is unable to generate cells of the primitive eryth roid lineage. Analysis of the cytokine responsiveness of the two lines with primitive erythroid potential has indicated that exposure to leu kemia inhibitory factor (LIF) results in the upregulation of beta H1 a nd a change in cellular morphology to that of primitive erythrocytes. These findings are the first demonstration of a clonal cell line with primitive and definitive hematopoietic potential and support the inter pretation that these lineages may arise from a common precursor in emb ryonic life. In addition, they suggest that LIF could play a role in t he regulation of primitive erythropoiesis. (C) 1998 by The American So ciety of Hematology.